Page 44 - Subyek Encyclopedia - Encyclopedia of Separation Science

Sepsci*11*TSK*Venkatachala=BG
I / CENTRIFUGATION 39

Figure 17 Multistage push-type centrifugal filter. (Courtesy of Alfa Laval Separations.)

drainage. Some designs incorporate a lower cone discharging designs. The cone angle is 13 to 183 with
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angle at the small end, where most of the drainage throughput capacities of 25}150 t h . Their most
occurs, and a higher angle on the large end, to in- common application is for the dewatering of coal
crease the solids-holding capacity and provide addi- Rnes.
tional drainage time.
Three methods of solids removal are commonly
used for conical Rltration: screw conveyer, self-dis- Acknowledgements
charging or vibratory. Screw conveyers consist of The authors wish to express their appreciation to Dr
a vertical or horizontal conical bowl with an internal Allen Furst (Beckman Inst., Inc.) and Mr John
helical screw rotating slightly faster than the conical McKenna (Alfa-Laval Sharples) for their helpful com-
drum. In this conRguration, solids are continually ments and timely review of this manuscript and to Ms
moved from the small end of the cone and discharged Kimberly Neumann (Alfa-Laval Sharples) and Ms
from the larger end. Screw-conveyer units have cone Joyce Pederson (Beckman Inst., Inc.) for provision of
angles that generally range from 10}203, feed capaci- several portions of the reprinted artwork. We would
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ties of 1}15 m h , and centrifugal forces to 3500g.
also like to acknowledge the support of the University
Applications include the dewatering of crystalline
of Kentucky Center for Applied Energy Research.
solids and the extraction of solids from fruit and
vegetable pulps. Self-discharging Rlters are similar to
screw conveyers, only the cone angle is larger See Colour Plate 2.
(20}353) than the angle of repose of the cake. At these
greater angles, the solids slide down the tapered walls Further Reading
and exit the large end of the conical drum without the
need for mechanical assistance. Vibratory-discharge Birnie GD and Rickwood D (eds) Centrifugal Separation in
Molecular and Cell Biology. London: Butterworths.
Rlters are also similar in design to screw-conveyer Brakke MK (1952) Density gradient centrifugation: a new
units, but in this case solids discharge is accomplished separation technique. Journal of the American Chemical
by applying a vibratory or oscillatory motion to the Society 73: 1847}1848.
bowl or casing. Such units are typically operated at Coulson JM, Richardson JF, Backhurst JR and Harker JH
low speeds (300}500 rpm) and used to process larger (1978) In: Chemical Engineering, 3rd edn, vol. 2: Unit
particles (0.25}30 mm) than screw-conveyer or self- Operations. Oxford: Pergamon Press.